White light is important in many lighting applications such as automotive headlamps, general lighting, photography, and microscope illumination. Inconsistency of the observed white color can result in undesirable shifts in appearance. Not all “white” light bulbs give out the same color white light. Labeling on currently available white bulbs may indicate “warm” white or “cool” white. The labeling is based on a correlated color temperature (CCT) rating. CCT indicates the expected color appearance, and it is a simplified representation of the spectral power distribution (SPD) for a given light source. By industry convention, a light source with a CCT in the 2700K to 3000K range provides a “warm” white light, while a light source with a CCT in the 4000K to 6500K range provides a “cool” white. After the desired white light color has been identified, bulbs that are currently available also have issues of color consistency between different bulbs having the same CCT ratings. Also, shifts in the observed color can occur during the lifetime of the light source as components age.
U.S. Patent Publication No. 2015/0252974 to Darwin Hu (“Hu”) discloses creating white light using two color sources. Hu describes green laser beams applied to excite a magenta phosphor substrate to create white light. However, the white color will still change as the phosphor ages, and as the color output of the blue LEDs changes with age.